It is common practice to supply compressed air to mines, building sites and through manufacturing plants via an air line of interconnecting pipes and hoses. Compressed air is used to operate machinery, such as packaging machines, rock drilling machines, and portable tools, and for starting some diesel mobile plant. It is a convenient, flexible, high energy source that can be quickly installed, used and dismantled as required.
The connection of the air line of pipes and hoses is via a range of quick connect couplers or bolted joints. A common coupler is a “claw” coupler, which allows an operator to “twist and lock” a hose onto an air supply valve, connect two hoses together, or connect a hose to a machine.
Air is controlled (i.e. turned on and off) by the use of isolation or control valves. These valves can be manually operated by hand, can be electrically controlled, or can be operated by other methods.
However, there are numerous problems and dangers associated with the use of compressed air. This is largely due to the flexible, high energy nature of compressed air which, when combined with poor practices, have, in the past, resulted in major injury and death.
Death has been attributed to impact injury (disconnected hoses flailing around), and compressed air injection into the bloodstream. Injuries associated with compressed air include air injection, and both temporary and permanent hearing loss.
The following method is an example of the use of compressed air as commonly occurs on a building site, and indicates some problems and dangers that exist both in normal use and when operators fail to follow normal practice.
A mobile air compressor is located adjacent a pit requiring excavation and remote from an operator. The problem here is that the source of compressed air and the control valve associated with the compressor are not located where the work is being carried out at the free end of the hose, and so if a fault arises, such as when a flexible hose ruptures, the compressed air cannot be quickly turned off.
The compressor is connected via a 50 m hose to a portable jack hammer. The operator connects the hose firstly to the compressor, then holds the free end of the hose whilst compressed air is used to purge or clean the flexible line.
This process requires the operator to connect the hose to the compressor and then fit a secondary (separate) locking clip. This locking clip is used to prevent inadvertent unlocking of the hoses caused by hose tension when turning on air supply. This can be due to the fact that hoses are delivered neatly coiled and, when air pressure is applied, the hose naturally untwists thus causing the “twist and lock” couplers to disconnect.
To purge or clean the hose requires the operator to travel to the compressor (where the air control valve is fitted) whilst holding the free end of the hose, or to involve another person near the compressor to turn the air supply on and off.
Although a 50 m hose is used in this example, in practice the compressor and jackhammer or other tool may be connected by 500 m or more of hose.
After purging the line, the operator connects the jack hammer, and turns on the air supply in order to remove the rock.
This process requires that, if the operator is by himself, he has to drag the hose to the jackhammer, connect up the tool using the secondary locking clip for safety, and then travel back to the compressor, once again, to turn the compressed air on, so work can begin. Whilst he is turning on the air supply, the operator is not at the tool site and therefore cannot see if any problems exist, e.g. air leaks or hose problems.
At completion of the job, the operator turns off the air, operates the jack hammer to dissipate the trapped air in the hose, or releases the air through a drain valve, then proceeds to disconnect the tool and hose from the compressor.
This process requires the operator to travel to the compressor and turn off the air, then travel back to the tool to release the trapped air in the hose, or release the air through the drain valve. Using the drain valve releases air at a high velocity, resulting in noise that may permanently damage hearing. This high velocity air, when directed at the ground, can cause loose debris (rocks and dust) to be violently blown around, sometimes resulting in impact injuries to the body or to the eyes in particular.
Once the tool is disconnected, there is a danger that the air supply may be unknowingly turned on allowing the free end of the hose to flail around uncontrollably.
Aside from the problems and dangers associated with the above method, operators may take shortcuts which can also give rise to problems and dangers. These shortcuts include:—                (a) use of a screwdriver or similar pointed tool to force the seal of the “claw” coupler apart to relieve the trapped pressure (instead of returning to the tool and operating it to exhaust air);        (b) engaging a second person to crimp off the hose using their hands whilst the operator disconnects and reconnects the hose. This is particularly hazardous as air is only isolated for the time the second person can continue to maintain the crushing force on the hose. If that person trips or their hand grip slips whilst holding the hose, then air is released with uncontrolled force and speed.        
Both (a) and (b) above can allow air to be released from a pressurised state quite rapidly, which will have the effect of generating a noise level that can cause permanent hearing loss.
Other steps taken to overcome the problems identified above are:                (c) Some operators fit control valves with manual lever handles at hose ends. This can create problems when air is turned off and not released out of the hose, as there is no indication that the hose contains trapped air under pressure. This can only be identified by operation of the machine, which can cause unexpected or unwanted movement. Also, when the hose is dragged from one site to another, the lever handle can be caught and the air unexpectedly turned on.        (d) Some operators fit venting valves at the compressor or source end of the air supply system. This does relieve the operator of some travel when removing the equipment from service, but still requires the operator to travel back to the source.        (e) Some operators fit control valves with provision for padlocking the valve in a closed position. This solves the problem when the distance between the source and the tool is relatively short, but does not fix it when there is considerable distance between the source and the tool.        (f) Some operators fit silencers to the fixed venting valves located at the compressor end of the hose, which effectively eliminates the hearing damage risk. This solves part of the problem but is impractical to fit in all situations.        
In summary, the problems encountered in the prior art include:                1. Control valves and tools are often a considerable distance apart, leading to shortcuts and non-adherence to normal practice.        2. Twist and lock couplers can become separated if the locking clip is not installed.        3. Locking clips are a separate item requiring the operator to carry them to safely do the job.        4. Hoses can be inadvertently uncoupled under pressure, as the presence of air pressure is not apparent and there is no interlock requiring the operator to release the pressure.        5. Venting devices fitted are sometimes remote from the tool.        6. Silencers fitted are sometimes remote of the tool.        7. Additional operators required if considerable distance between compressor and tool.        
It is, therefore, an object of the present invention to overcome at least some of the aforementioned problems of the prior art.